i8042.nopnp is essentially a kernel boot parameter. Not sure it's a real problem, but it does suggest adding it at boot....meaning add to Grub. Note, it's a suggestion...not technically an error. You could certainly try it.

Similar to adding NOMODESET, use edit or "e" to grub menu selection line at boot for a simple one-time test. You locate and add the parameter after "quiet splash", e.g.

"...... quiet splash i8042.nopnp".

If that works (and you really want to go forward), you could add the parm to /etc/default/grub file and run the following from Terminal to make it permanent.

The reason I am asking is because on rare occasions my PS/2 keyboard will be non-functional
upon booting. If I just reboot it will then again function normally.

I use PS/2 keyboard but I use USB optical mouse.

I found some info after making this post that seems to suggest to me that this is perhaps
a flaw in the Linux kernel that my current version of Mint is using and I am now wondering
if moving from version 18.1 to 18.3 and the new kernel associated with 18.3 would solve
this problem. What do you think ?

Also, am sort of wondering what the message is referring to when it mentions the AUX port being disabled.
Is this possibly referring to the fact that I am using the PS/2 port for keyboard but that the PS/2 port
for mouse is not being used / empty, i.e. no device. But if this is the case why would it NOT work
all the time and not just on rare occasions.

Yes, the message does (as far as I can tell) seem to coincide with the occurrence of the non-functioning of
the keyboard.

No, I don't really have a proper keyboard to use for testing. I have some cheap USB keyboards but I do
not like the layout & feature set of them. And even if I had a proper substitute keyboard this problem only
seems to happen on VERY RARE occasions even with my normal PS/2 keyboard. This problem might only
happen 1 time out of 100 or more boots.

wpshooter wrote:I found some info after making this post that seems to suggest to me that this is perhaps
a flaw in the Linux kernel that my current version of Mint is using and I am now wondering
if moving from version 18.1 to 18.3 and the new kernel associated with 18.3 would solve
this problem. What do you think ?

I'm not thinking a Kernel update would help, but you could certainly test a newer kernel without update to Mint 18.3. Kernel 4.10 is bundled with Mint 18.3, but is no longer being patched/fix. Kernel 4.13 is getting patched, as is your current Kernel 4.4 (which is a Long-Term-Support/LTS Kernel). Those newer Kernels can be installed from Update Manager. Look in the drop-list under View. Note, the most current Kernel boots unless you override from grub menu.

wpshooter wrote:Also, am sort of wondering what the message is referring to when it mentions the AUX port being disabled.
Is this possibly referring to the fact that I am using the PS/2 port for keyboard but that the PS/2 port
for mouse is not being used / empty, i.e. no device. But if this is the case why would it NOT work
all the time and not just on rare occasions.

That's probably a better question in regards to what's happening. I do think the AUX port is the mouse. At least that's what my checks confirm. If so, the message "PS/2 appears to have AUX port disabled" is correct, so the advise is actually contrary to that condition, and may imply no action is needed. The keyboard failing to detect could be a fault/failing PS/2 port or keyboard that's pushing the message to occur. Given that quirks list, I'm more incline to suggest this one to stop Aux port check:

i8042.noaux - Don't check for auxiliary (== mouse) port

You could test the i8042.noaux for grub override as a test. At least see if the message disappears. My original post has the method to add for test from Grub Menu.

Edit: Sanity Check! Make sure the keyboard is connected to PS/2 keyboard port and NOT the PS/2 mouse port.

Am going to trying changing to Mint version 18.3 AFTER I get my
tax return prep done for this year and see if new version might take care
of the problem and if not, I will give the editing of grub a try.

i8042: PNP: PS/2 appears to have AUX port disabled, if this is incorrect please boot with i8042.nopnp

However, my PS/2 keyboard comes up as non-functional only on very rare occasions.

So what does this message really mean and should I try the NONPNP boot / grub parameter to see if
that will stop this occasional non-functioning problem with my keyboard OR is this just a slight flaw on
the PS/2 connector on the motherboard ?

Am going to switch to a USB keyboard and see if this same message is still generated in the log file.

Hmmmmmmmmmm, just switched over to a cheap USB keyboard that I have and the PNP message did
not appear in the log, so it appears that this message is basically only telling me that if I have a PS/2 keyboard
plugged in the socket and I am using a USB mouse, that the keyboard is using PS/2 but that there is NO mouse
on the mouse PS/2 port.

So, this really does not solve why I am on rare occasions getting a non-functional PS/2 keyboard when I
get booted up to the desktop.

1) Problem with motherboard PS/2 port. Could be chipset or power problem. If it happens most on a cold boot, could be weak/old power supply until warmed-up.

2) Problem with keyboard's internal chip and keyboard is headed to failure.

3) If it's an old AT Keyboard and you're using an AT-to-PS/2 adapter, those sometimes have problems.

Thanks for your reply.

This is happening on 2 different Keytronic (not exactly junk keyboards). One of them is fairly new hardly used.
This does not seem to be related to cold boot because it can happen when machine is booted initially after
a period of non-use (so to speak cold) or when machine is warmed (say if I do a reboot for some reason).

No, am not using an adapter, keyboards are being plugged directly into the PS/2 port.

On what little time I have tested using a USB keyboard, I have yet to have a non-functional keyboard when
I get to the desktop.

I am leaning toward an intermittent problem with the PS/2 port itself. If this is it, just wondering what would
cause this problem.

If it is the PS/2 port, could be a failure in motherboard chip. Also, might look for any BIOS updates for the motherboard. I'm assuming there are no messages during post that point to keyboard error. Dell systems sometime track keyboard errors in BIOS log. Actually, had that problem with keyboard going bad on older Dell system, and the the log did track it.

If it is the PS/2 port, could be a failure in motherboard chip. Also, might look for any BIOS updates for the motherboard. I'm assuming there are no messages during post that point to keyboard error. Dell systems sometime track keyboard errors in BIOS log. Actually, had that problem with keyboard going bad on older Dell system, and the the log did track it.

There are no keyboard messages in the BIOS even though I DO have the BIOS parameter for keyboard errors enabled.

This is a fairly old Dell Optiplex and there is no recent update (beyond what I am using) to the BIOS. I have talked to Dell until I am blue in the face
trying to see if they are going to put out a new BIOS to fix the recent Spectre and Meltdown issues, I think I am wasting my time.

I talked to Keytronics keyboard support this morning and the girl there seemed to think that this is some type of TIMING issue
that is happening during hardware detection during initial boot sequencing. My guess is that she is correct. She advised
switching to one of their USB keyboards. I tend to agree with her analysis.

Depends on which processor you have, as to whether it will get a BIOS/microcode fix for Meltdown/Spectre. I doubt Dell will update BIOS on anything older than 5 years and Intel might not fix anything older than that either.

Edit: Any chance your BIOS has a setting for delay for drive detection that might help?

Edit2: I did think of another possible way to get the keyboard to work. However, you'll have to check with the manufacturer. A PS/2 to USB adapter might fix the problem, if the keyboard can work with the adapter.